A method of fabricating a solar cell for solar light power generation is as follows. First, after preparing a substrate, a back electrode layer is formed on the substrate. Thereafter, a light absorbing layer, a buffer layer, and a high resistance buffer layer are sequentially formed on the back electrode layer. Various schemes, such as a scheme of forming a Cu(In,Ga)Se2 (CIGS) based-light absorbing layer by simultaneously or separately evaporating Cu, In, Ga, and Se and a scheme of performing a selenization process after a metallic precursor film has been formed, have been extensively used in order to form the light absorbing layer. The energy bandgap of the light absorbing layer is in the range of about 1 eV to 1.8 eV.
Then, a buffer layer including cadmium sulfide (CdS) is formed on the light absorbing layer through a sputtering process. The energy bandgap of the buffer layer may be in the range of about 2.2 eV to 2.4 eV. After that, a high resistance buffer layer including zinc oxide (ZnO) is formed on the buffer layer through the sputtering process. The energy bandgap of the high resistance buffer layer is in the range of about 3.1 eV to about 3.3 eV.
Then, a transparent electrode layer is formed on the high resistance buffer layer, and a transparent electrode layer is formed on the high resistance buffer layer. A material constituting the transparent electrode layer may include aluminum doped zinc oxide (AZO). The energy bandgap of the transparent electrode layer may be in the range of about 3.1 eV to about 3.3 eV.
Many studies and researches have been performed to improve photoelectric conversion efficiency by adjusting a bandgap energy in the light absorbing layer in the photovoltaic apparatus.
As described above, in order to convert the solar light into electrical energy, various photovoltaic apparatuses have been fabricated and used. One of the photovoltaic apparatuses is disclosed in Korean Unexamined Patent Publication No. 10-2008-0088744.